Control valve for variable displacement compressor

ABSTRACT

To provide a control valve for a variable displacement compressor, which is capable of promptly restoring a high-sensitivity variable displacement compressor to a predetermined discharge capacity without causing hunting even when the rotational speed of the compressor is rapidly changed. A valve section controls the flow rate of refrigerant flowing from a discharge chamber to a crankcase, based on the differential pressure between discharge pressure and suction pressure. A pressure-sensing section is provided in a high-pressure port, and when a pressure-sensing piston having a pressure-receiving area larger than that of a valve element is exposed to a rapid change in the discharge pressure, the differential pressure generated between the discharge pressure and pressure in a pressure-adjusting chamber acts on the valve element in a direction opposite to a valve-opening/closing direction, to thereby temporarily make slower the motion of the valve element which is to be opened or closed by the differential pressure between the discharge pressure and the suction pressure. This makes it possible to promptly restore a high-sensitivity variable displacement compressor to a predetermined discharge capacity without hunting.

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY

This application claims priority of Japanese Application No. 2004-251287 filed on Aug. 31, 2004 and entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR” and No. 2005-021518 filed on Jan. 28, 2005, entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor, which is mounted on a variable displacement compressor as a component of a refrigeration cycle of an automotive air conditioner, for control of the discharge capacity of the compressor by the differential pressure between discharge pressure and suction pressure.

(2) Description of the Related Art

A compressor used in the refrigeration cycle of an automotive air conditioner, for compressing refrigerant, uses an engine as a drive source, and hence is incapable of performing rotational speed control. To eliminate the inconvenience, a variable displacement compressor capable of varying the compression capacity of refrigerant is employed so as to obtain an adequate cooling capacity without being constrained by the rotational speed of the engine.

In such a variable displacement compressor, a wobble plate fitted on a shaft driven by the engine for rotation has compression pistons connected thereto, and by varying the inclination angle of the wobble plate, the stroke of the pistons is varied to vary the discharge amount of refrigerant.

The inclination angle of the wobble plate is continuously changed by introducing part of compressed refrigerant into a hermetically closed crankcase, and causing a change in the pressure of the introduced refrigerant, thereby changing the balance of pressures acting on the opposite sides of each piston.

A control valve for a variable displacement compressor is known (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2001-132650 (Paragraph numbers [0043] to [0045], FIG. 4)) which is disposed between a discharge chamber and a crankcase of the compressor, or between the crankcase and a suction chamber of the compressor, for adjusting pressure in the crankcase by changing the flow rate of refrigerant introduced from the discharge chamber into the crankcase, or changing the flow rate of refrigerant delivered from the crankcase to the suction chamber.

The control valve described in Japanese Unexamined Patent Publication (Kokai) No. 2001-132650 is configured such that it has a valve section disposed in a refrigerant passage between the discharge chamber and the crankcase of the compressor when it is mounted in the compressor, and a path is formed along which refrigerant flows from the discharge chamber to the suction chamber of the compressor via an orifice provided between the crankcase and the suction chamber. The control valve has the valve section which comprises a valve element that receives discharge pressure Pd in the valve-opening direction, and a piston rod that is integrally formed with the valve element on a rear side of the valve element and has approximately the same diameter as that of a valve hole, and is configured such that an end face of the piston rod receives suction pressure Ps and the load of a solenoid for setting the discharge capacity of the compressor by an external signal, in the valve-closing direction. Therefore, in this control valve, the discharge pressure Pd and the suction pressure Ps are received by the opposite ends of the valve element and piston rod, both having the same effective pressure-receiving area, and hence the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps causes the valve element to perform an opening/closing operation to thereby control the flow rate of refrigerant flowing from the discharge chamber into the crankcase.

For example, as the rotational speed of the compressor increases with an increase in the rotational speed of the engine to cause an increase in the discharge capacity of the compressor, the discharge pressure Pd increases and the suction pressure Ps decreases to increase the differential pressure (Pd−Ps). This increases the valve lift of the valve section which operates depending on the differential pressure (Pd−Ps), so that the control valve increases the flow rate of refrigerant being introduced into the crankcase to increase pressure Pc in the crankcase, which decreases the discharge capacity of the compressor, thereby decreasing the differential pressure (Pd−Ps). In short, the control valve controls the flow rate of refrigerant being introduced into the crankcase such that the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps is held at a predetermined value. The predetermined value of the differential pressure can be set from outside by a value of electric current supplied to the solenoid.

In the above compressor controlled by the control valve, a change in the rotational speed of the engine changes the rotational speed of the compressor to change the discharge capacity of the compressor. This change in the discharge capacity changes the differential pressure (Pd−Ps) to change the pressure Pc in the crankcase, whereby the inclination angle of the wobble plate is changed to vary the discharge capacity between the maximum and minimum capacities. For example, when the differential pressure (Pd−Ps) is zero as at the start of the compressor, the compressor operates with the maximum capacity, and when the differential pressure (Pd−Ps) reaches a certain value, the capacity starts to be varied. However, each individual variable displacement compressor has a character of its own, and the differential pressure (Pc-Ps) between the pressure Pc in the crankcase and the suction pressure Ps at the start of varying the discharge capacity has a range of values varying depending on the compressor. This is caused by the difference in mobility of the wobble plate, that is, the difference in sensitivity between compressors.

However, a high-sensitivity variable displacement compressor suffers from the problem of reacting sensitively to rapid changes in the discharge pressure Pd and the suction pressure Ps caused by a sudden change in the rotational speed of the engine, resulting in hunting.

SUMMARY OF THE INVENTION

The present invention has been made in view of the problem, and an object thereof is to provide a control valve for a variable displacement compressor, which is capable of controlling the variable displacement compressor having high sensitivity stably without causing hunting, even when a rapid change in pressure is caused by a sudden change in the rotational speed of the engine.

To solve the above problem, the present invention provides a control valve for a variable displacement compressor, which is configured to sense differential pressure between discharge pressure in a discharge chamber of the compressor and suction pressure in a suction chamber of the compressor, and control a flow rate of refrigerant allowed to flow from the discharge chamber into a crankcase to thereby change a discharge capacity of the refrigerant, comprising a pressure-sensing section that senses a change in pressure caused by a rapid change in a rotational speed of the compressor and makes a motion of a valve section in a valve-opening/closing direction slower by a value proportional to a degree of the change in pressure.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a first embodiment of the present invention.

FIG. 2 is a diagram useful in explaining operation of the control valve, in the case where the rotational speed of the compressor is rapidly increased.

FIG. 3 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a second embodiment of the present invention.

FIG. 4 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a third embodiment of the present invention.

FIG. 5 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fourth embodiment of the present invention.

FIG. 6 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fifth embodiment of the present invention.

FIG. 7 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a sixth embodiment of the present invention.

FIG. 8 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a seventh embodiment of the present invention.

FIG. 9 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to an eighth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a first embodiment of the present invention.

The control valve 11 comprises a pressure-sensing section 12 that senses a rapid change in discharge pressure Pd, a valve section 13 that senses the differential pressure (Pd−Ps) between the discharge pressure Pd and suction pressure Ps to control the flow rate of refrigerant allowed to flow from a discharge chamber into a crankcase, and a solenoid 14 that is capable of setting a predetermined value to which the differential pressure (Pd−Ps) is to be controlled by the control valve, from outside, these sections being arranged on the same axis.

A body 15 containing the pressure-sensing section 12 and the valve section 13 has an upper part thereof, as views in FIG. 1, formed with a cylinder 16, and an upper end thereof formed with an opening closed by a lid 17. A high-pressure port 18 which communicates with the discharge chamber when the control valve 11 is mounted in the variable displacement compressor is formed in the body at a location below the cylinder 16, as viewed in FIG. 1. A pressure-sensing piston 19 is disposed within the cylinder 16 in a manner movable axially back and forth, and a space for a pressure-adjusting chamber 20 is defined in an upper portion of the cylinder 16, together with the body 15 and the lid 17. The pressure-adjusting chamber 20 is configured to communicate with the high-pressure port 18 via a predetermined clearance between the cylinder 16 and the pressure-sensing piston 19. The cylinder 16 has a hole formed in the center of a bottom thereof, and a hollow cylindrical valve seat-forming member 21 is press-fitted in the hole. The valve seat-forming member 21 has a passage, i.e. a valve hole axially extending therethrough, and a lower end, as viewed in FIG. 1, which forms a valve seat of the valve section 13. Further, a shaft 22 extends through the valve hole formed through the valve seat-forming member 21, and one end of the shaft 22 is fixed to the pressure-sensing piston 19.

A valve element 23 is disposed in a manner opposed to the valve seat formed by the valve seat-forming member 21 such that it can open and close the valve hole. The valve element 23 is integrally formed with the shaft 22 having one end thereof fixed to the pressure-sensing piston 19 and a piston rod 24 held by the body 15 in a manner movable axially back and forth. The piston rod 24 is formed such that it has an outer diameter equal to the inner diameter of the valve hole of the valve seat-forming member 21. Further, the piston rod 24 is urged by a spring 25 in a direction in which the valve element 23 is moved away from the valve seat-forming member 21. It should be noted that a space where the valve element 23 is disposed communicates with a medium-pressure port 26 for supplying pressure Pc to the crankcase of the compressor when the control valve 11 is mounted in the compressor, and a space where the spring 25 is disposed communicates with a low-pressure port 27 for receiving the suction pressure Ps from a suction chamber.

The body 15 has a hole formed in the center of a lower part thereof, as viewed in FIG. 1. The rim of an opening of a bottomed sleeve 28 is tightly connected to the hole. The bottomed sleeve 28 has a core 29 and a plunger 30 of the solenoid 14 arranged therein. The core 29 is fixed to the hole in the center of the lower part of the body 15 and the bottomed sleeve 28 by press-fitting. The plunger 30 is axially slidably disposed in the bottomed sleeve 28, and fixed to one end of a shaft 31 disposed in a manner axially extending through the core 29. Further, the plunger 30 is urged toward the core 29 by a spring 32 such that the other end of the shaft 31 is brought into abutment with a lower end face of the piston rod 24, as viewed in FIG. 1. Disposed around the outer periphery of the bottomed sleeve 28 is a coil 33, and a harness 34 for supplying electric current to the coil 33 is led to the outside of the solenoid 14.

In the control valve 11 constructed as above, the spring 25 urging the piston rod 24 of the valve section 13 toward the solenoid 14 is set to have a larger spring load than that of the spring 32 urging the shaft 31 of the solenoid 14 toward the valve section 13. Therefore, when the solenoid 14 is deenergized, the valve element 23 of the valve section 13 is away from the valve seat-forming member 21, and hence the valve section 13 is held in the fully open state. At this time, high-pressure refrigerant at the discharge pressure Pd, which has been introduced from the discharge chamber of the compressor to the high-pressure port 18, passes through the valve section 13 in the fully open state, and flows from the medium-pressure port 26 into the crankcase. This makes the pressure Pc in the crankcase close to the discharge pressure Pd, whereby the compressor is caused to operate with the minimum discharge capacity.

When an automotive air conditioner is started or when the cooling load is maximum, the value of electric control current supplied to the solenoid 14 is maximum. At this time, the plunger 30 is attracted with the maximum attractive force by the core 29, so that the piston rod 24 of the valve section 13 is pushed by the shaft 31 fixed to the plunger 30, in the valve-closing direction against the urging force of the spring 25, whereby the valve element 23 is seated on the valve seat-forming member 21 to place the valve section 13 in the fully closed state. At this time, the high-pressure refrigerant at the discharge pressure Pd, introduced into the high-pressure port 18, is blocked by the valve section 13 in the fully closed state, which makes the pressure Pc in the crankcase close to the suction pressure Ps, whereby the compressor is caused to operate with the maximum discharge capacity.

Now, when the value of electric current supplied to the solenoid 14 is set to a predetermined value, the valve element 23 is stopped at a valve lift position where the load of the spring 25 urging the valve element 23 in the valve-opening direction, the load of the solenoid 14 urging the valve element 23 in the valve-closing direction, the discharge pressure Pd which the valve element 23 receives in the valve-opening direction, and the suction pressure Ps which the valve element 23 receives in the valve-closing direction are balanced.

In the above balanced state, when the rotational speed of the compressor is increased e.g. by an increase in the rotational speed of the engine, to increase the discharge capacity of the compressor, the discharge pressure Pd increases and the suction pressure Ps decreases so that the differential pressure (Pd−Ps) increases to cause a force in the valve-opening direction to act on the valve element 23 and the piston rod 24, whereby the valve element 23 is lifted from the balanced position, thereby allowing refrigerant to flow from the discharge chamber into the crankcase at an increased flow rate. As a result, the pressure Pc in the crankcase is increased to cause the compressor to operate in a direction in which the discharge capacity thereof is reduced, whereby the differential pressure (Pd−Ps) is controlled to the predetermined value set by the solenoid 14. When the rotational speed of the engine has decreased, the control valve operates oppositely to the above, whereby the compressor is controlled such that the differential pressure (Pd−Ps) becomes equal to the predetermined value set by the solenoid 14.

As described above, when the rotational speed of the compressor is being gently changed as in the case where an automotive vehicle is cruising at an approximately constant speed, the pressure-sensing section 12 is insensitive, and performs the same operation as that of the conventional control valve for a variable displacement compressor. Next, a description will be given of operation of the control valve 11 in the case where the rotational speed of the compressor is rapidly changed by a rapid change in the rotational speed of the engine as in the case where the automotive vehicle has been suddenly accelerated or decelerated.

FIG. 2 is a diagram useful in explaining operation of the control valve for a variable displacement compressor, in the case where the rotational speed of the compressor is rapidly increased.

When the compressor is stably operating e.g. at a rotational speed of 800 rpm, if the rotational speed has been increased up to a rotational speed of 2000 rpm, the valve lift is increased due to a rise in the discharge pressure Pd and a drop in the suction pressure Ps, whereby the control valve 11 increases the pressure Pc in the crankcase. At this time, in the compressor with higher sensitivity, as indicated by broken lines in FIG. 2, overshoots of the valve lift, the discharge pressure Pd, the pressure Pc in the crankcase, and the suction pressure Ps tend to occur, causing a hunting phenomenon.

When the overshoots occur, the pressure-sensing section 12 receives the discharge pressure Pd, which has rapidly increased, at the pressure-sensing piston 19 having a sufficiently larger pressure-receiving area than that of the valve element 23. In contrast, in the pressure-adjusting chamber 20, pressure Pd(av), which is average pressure of the discharge pressure Pd before it has rapidly increased, is maintained, and hence the differential pressure (Pd−Pd(av)) generates a force which acts on the pressure-sensing piston 19 in a direction in which the valve element 23 is moved away from the valve section 13. This force is transmitted to the valve element 23 via the shaft 22, a force obtained by subtracting the differential pressure (Pd−Pd(av)) acting on the pressure-sensing section 12 from the rapidly increased discharge pressure Pd is applied to the valve element 23. As a result, as indicated by solid lines in FIG. 2, the valve lift is increased more slowly, so that the control valve 11 causes the pressure Pc in the crankcase to increase more slowly. After that, in the pressure-sensing section 12, the rapidly increased discharge pressure Pd is promptly introduced into the pressure-adjusting chamber 20 via the clearance between the cylinder 16 and the pressure-sensing piston 19, whereby the differential pressure (Pd−Pd(av)) becomes equal to zero. At this time, the function of the pressure-sensing section 12 has been lost. This means that the pressure-sensing section 12 has the function of sensing a rapid increase in the discharge pressure Pd, and temporarily making the motion of the valve section 13 in the valve-opening direction slower by a value proportional to the degree of the change in pressure. This enables the control valve 11 to promptly restore the compressor to the predetermined discharge capacity without causing any hunting.

Although the above description has been given of the operation of the control valve 11 in the case of the rotational speed of the compressor being rapidly increased, the control valve 11 operates similarly when the rotational speed of the compressor is rapidly decreased. More specifically, when the rotational speed of the compressor is rapidly decreased, the differential pressure (Pd(av)−Pd) acting on the pressure-sensing section 12 serves as a force for moving the pressure-sensing piston 19 toward the valve section 13. Therefore, the differential pressure (Pd−Pd(av) serves as a force for temporarily urging the valve element 23, which is about to move in the valve-closing direction, in the valve-opening direction. Thus, also when the rotational speed of the compressor is rapidly decreased, the control valve 11 operates in a quite an opposite way compared with the case of the rotational speed of the compressor being rapidly increased.

In the control valve constructed as above, the pressure-sensing piston 19 may be provided with flow rate-adjusting means, such as a piston ring, which has a portion circumferentially cut off to a predetermined length, to adjust the size of a passage via which refrigerant flows into or out of the pressure-adjusting chamber 20 to thereby control the characteristics of the pressure-sensing section 12.

FIG. 3 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a second embodiment. In FIG. 3, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 according to the first embodiment which is configured to sense a rapid change in the discharge pressure Pd for control of the valve lift of the valve section 13, the control valve 11 a according to the second embodiment is configured to sense a rapid change in pressure Pc supplied to the crankcase for control of the valve lift of the valve section 13.

To this end, in the control valve 11 a according to the second embodiment, the pressure-sensing section 12 is disposed in a space communicating with the medium-pressure port 26, and the pressure-sensing piston 19 that receives the pressure Pc is fixed to the piston rod 24 integrally formed with the valve element 23. The valve seat-forming member 21 has a flange portion that is fitted in an opening formed in an upper end of the body 15, as viewed in FIG. 3. The pressure-sensing piston 19 is loosely fitted in the body 15 at a location below the valve seat-forming member 21 in a manner movable axially back and forth, and an annular space of the pressure-adjusting chamber 20 is defined by the body 15 and the flange portion of the valve seat-forming member 21. Further, the pressure-sensing piston 19 has a recess formed in the center of an upper part thereof, and the recess is formed with a communication hole such that the recess communicates with the space communicating with the medium-pressure port 26 via the communication hole.

When the control valve 11 a constructed as above is controlling the compressor at a predetermined valve lift, if the discharge pressure Pd rapidly increases, and the suction pressure Ps rapidly decreases, the differential pressure (Pd−Ps) between the opposite ends of the valve element 23 and the piston rod 24 increases, whereby the valve lift is about to increase. This causes the pressure Pc on the downstream side of the valve section 13 as well to rapidly increase. At this time, since the pressure-sensing piston 19 of the pressure-sensing section 12 has a sufficiently larger pressure-receiving area than that of the valve element 23, a force is generated, which acts on the pressure-sensing piston 19 in a direction for temporarily moving the same upward, as viewed in FIG. 3, and the force causes the piston rod 24 fixed to the pressure-sensing piston 19 to act in the valve-closing direction. Therefore, the force acting on the pressure-sensing piston 19 in the valve-closing direction acts on the valve element 23, which is about to be moved in the valve-opening direction by the increased differential pressure (Pd−Ps), in an opposite direction to the direction of movement or lift of the valve element 23, and hence the valve lift is slowly increased, and the discharge pressure Pd and the pressure Pc in the crankcase are also slowly increased in accordance with the slow increase in the valve lift. In a short time, when the pressure in the pressure-adjusting chamber 20 becomes equal to the pressure Pc in the crankcase, the discharge pressure Pd, the pressure Pc in the crankcase, the suction pressure Ps, and the valve lift promptly return to their original states without causing overshoots. Of course, similarly, also when the rotational speed of the compressor is rapidly decreased, the control valve 11 a operates slowly to thereby make it possible to promptly restore the compressor to the predetermined discharge capacity.

FIG. 4 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a third embodiment of the present invention. In FIG. 4, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 according to the first embodiment which is configured to sense a rapid change in the discharge pressure Pd for control of the valve lift of the valve section 13 and the control configured to sense a rapid change in the pressure Pc supplied to the crankcase for control of the valve lift of the valve section 13, the control valve 11 b according to the third embodiment is configured to sense a rapid change in suction pressure Ps for control of the valve lift of the valve section 13.

To this end, in the control valve 11 b, the pressure-sensing piston 19 is disposed in a manner blocking a space having the spring 25 disposed therein and communicating with the low-pressure port 27 and a space communicating with the solenoid 14, and the pressure-sensing piston 19 is fixed to the piston rod 24 integrally formed with the valve element 23. Therefore, in the control valve 11 b, a space defined by the body 15, the pressure-sensing piston 19, the piston rod 24, the core 29, and the shaft 31 forms the pressure-adjusting chamber 20.

When the control valve 11 b constructed as above is controlling the compressor at a predetermined valve lift, if the discharge pressure Pd rapidly increases, and the suction pressure Ps rapidly decreases, the differential pressure (Pd−Ps) between the opposite ends of the valve element 23 and the piston rod 24 increases, whereby the valve lift increases. This causes the suction pressure Ps to rapidly decrease. At this time, since the pressure-sensing piston 19 of the pressure-sensing section 12 has a sufficiently larger pressure-receiving area than that of the valve element 23, a force is generated which acts on the pressure-sensing piston 19 in a direction in which the same is moved upward, as viewed in FIG. 4, and the force causes the piston rod 24 fixed to the pressure-sensing piston 19 to act in the valve-closing direction. The force of the pressure-sensing piston 19 in the valve-closing direction acts on the valve element 23, in an opposite direction to the direction of lift of the valve element 23, and hence the valve lift is slowly increased, to cause the discharge pressure Pd and the pressure Pc in the crankcase to also slowly increase. In a short time, when the pressure in the pressure-adjusting chamber 20 becomes equal to the suction pressure Ps, the discharge pressure Pd, the pressure Pc in the crankcase, the suction pressure Ps, and the valve lift promptly return to their original states without causing overshoots. Of course, similarly, also when the rotational speed of the compressor is rapidly decreased, the control valve 11 b operates slowly to thereby make it possible to promptly restore the compressor to the predetermined discharge capacity.

FIG. 5 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fourth embodiment of the present invention. In FIG. 5, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 according to the first embodiment in which the pressure-sensing section 12 senses rapid changes in the discharge pressure Pd in an increasing direction and a decreasing direction for control of the valve lift of the valve section 13, in the control valve 11 c according to the fourth embodiment, the pressure-sensing section 12 does not sense a rapid change in the discharge pressure Pd in the increasing direction but sensitively senses a rapid change in the discharge pressure Pd in the decreasing direction for control of the valve lift of the valve section 13.

More specifically, in the control valve 11 c, the pressure-sensing piston 19 as a component of the pressure-sensing section 12 is provided with a check valve mechanism (sensitivity-switching means) for switching sensitivity between when a rapid change occurs in the discharge pressure Pd in the increasing direction and when a rapid change occurs in the same in the decreasing direction. The check valve mechanism is formed by forming a passage with a stepped portion in the pressure-sensing piston 19 for communication between the high-pressure port 18 and the pressure-adjusting chamber 20, disposing a ball-shaped valve element 41 in a large-diameter passage toward the pressure-adjusting chamber 20, and holding a leaf spring 42 in an open end of the passage toward the pressure-adjusting chamber 20 so as to prevent the valve element 41 from being removed into the pressure-adjusting chamber 20.

When the control valve 11 c constructed as above is controlling the compressor at a predetermined valve lift, if the discharge pressure Pd rapidly increases, the check valve mechanism provided in the pressure-sensing piston 19 is immediately opened by the differential pressure between the discharge pressure Pd and the pressure in the pressure-adjusting chamber 20, to thereby reduce the differential pressure to zero. As a result, the pressure-sensing section 12 is placed in an insensitive state, so that the valve section 13 acts rapidly in the valve-opening direction in a manner sensitively responsive to the rapid increase in the discharge pressure Pd, thereby causing the pressure Pc in the crankcase to rise more promptly such that the discharge capacity of the compressor is promptly controlled in the decreasing direction.

Inversely, if the discharge pressure Pd has rapidly decreased, the check valve mechanism provided in the pressure-sensing piston 19 is closed by the differential pressure between the rapidly-lowered discharge pressure Pd and pressure Pd(av) in the pressure-adjusting chamber 20, which is average pressure of the discharge pressure Pd before it has rapidly decreased, so that the pressure-sensing piston 19 having a larger pressure-receiving area than that of the valve element 23 sensitively detects the change in the rapidly-lowered discharge pressure Pd. Although the valve element 23 attempts to act in the valve-closing direction in response to the rapid decrease in the discharge pressure Pd, since the pressure-sensing piston 19 instantaneously acts in the valve-opening direction in response to the rapid change in the discharge pressure Pd, the valve element 23 is made slower in its action in the valve-closing direction. This means that the control valve 11 c has asymmetric valve-opening characteristics that it has a high sensitivity to a rapid change in the discharge pressure Pd in the increasing direction, whereas it has a low sensitivity to a rapid change in the discharge pressure Pd in the decreasing direction. Therefore, e.g. even if the compressor performs an excessive response to a rapid change in the discharge pressure Pd in the increasing direction to cause the discharge pressure Pd to rapidly change in the decreasing direction, the compressor is prevented from performing an excessive response to a rapid change in the discharge pressure Pd in the decreasing direction. This prevents occurrence of a hunting phenomenon.

FIG. 6 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fifth embodiment of the present invention. In FIG. 6, component elements identical to those shown in FIG. 5 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 c according to the fourth embodiment in which the check valve mechanism of the pressure-sensing section 12 is provided in the pressure-sensing piston 19, and the valve element of the check valve is formed by a ball-shaped valve, in the control valve 11 d according to the fifth embodiment, the check valve mechanism of the pressure-sensing section 12 is provided in the lid 17, and the valve element of the check valve is formed by a poppet valve.

More specifically, in the control valve 11 d, the check valve mechanism provided in the pressure-sensing section 12 is formed by forming a passage with a stepped portion in the lid 17 of the pressure-sensing section 12 so as to communicate between a space for receiving the discharge pressure Pd and the pressure-adjusting chamber 20, disposing a valve element 41 in the form of a mushroom in a large-diameter passage toward the pressure-adjusting chamber 20, fixedly engaging the leaf spring 42 in an open end of the passage toward the pressure-adjusting chamber 20 such that the valve element 41 is prevented from being removed into the pressure-adjusting chamber 20, and further disposing a sprig 43 having a small load for urging the pressure-sensing piston 19 in a direction away from the lid 17 between the lid 17 and the pressure-sensing piston 19.

The operation of the control valve lid including the pressure-sensing section 12 constructed as above is the same as the operation of the control valve 11 c according to the fourth embodiment. It should be noted that although in the fifth embodiment, the check valve mechanism is provided in the lid 17 of the pressure-sensing section 12, it may be provided in the body 15 isolating the pressure-adjusting chamber 20 from a side exposed to the discharge pressure Pd.

FIG. 7 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a sixth embodiment of the present invention. In FIG. 7, component elements identical to those shown in FIG. 6 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valves 11 c and 11 d according to the fourth and fifth embodiments which have the check valve mechanism, the control valve 11 e according to the sixth embodiment includes a sensitivity-switching mechanism which is capable of switching sensitivity between when the discharge pressure Pd rapidly increases and when the same rapidly decreases.

More specifically, in the control valve 11 e, the sensitivity-switching mechanism provided in the pressure-sensing section 12 switches ease of flow of refrigerant flowing into or out of the pressure-adjusting chamber 20, and the outer peripheral shape of the pressure-sensing piston 19 is formed into a tapered shape in which the outer diameter of the pressure-sensing piston progressively increases from the side toward the high-pressure port 18 to the pressure-adjusting chamber 20. Therefore, a gap between the outer periphery of the pressure-sensing piston 19 and the body 15 provides a narrowest restriction at an upper end of the gap in the pressure-adjusting chamber 20, as viewed in FIG. 7, and is progressively increased in passage cross-sectional area from the restriction to a space communicating with the high-pressure port 18. Assuming that the cross-sectional area of the refrigerant passage is hugely expanded on the high-pressure port side of the restriction, and refrigerant flows from the restriction into the hugely-expanded portion, a contracted flow is produced there. Insofar as the differential pressure between pressure in the high-pressure port 18 and pressure in the pressure-adjusting chamber 20 is the same, the pressure-sensing section 12 has a characteristic that the flow rate of refrigerant is smaller when refrigerant in the pressure-adjusting chamber 20 flows to the high-pressure port 18 after being abruptly restricted in flow by the restriction than when refrigerant in the high-pressure port 18 flows into the pressure-adjusting chamber 20 through the restriction after being progressively restricted in flow.

When the rotational speed of the compressor is rapidly increased to thereby rapidly increase the discharge pressure Pd. refrigerant is about to flow from a side toward the high-pressure port 18 into the pressure-adjusting chamber 20 through the gap between the outer periphery of the pressure-sensing piston 19 and the body 15, by the difference in pressure between the increased pressure in the high-pressure port 18 and the pressure in the pressure-adjusting chamber 20 before it is increased. Inversely, when the rotational speed of the compressor is rapidly decreased to rapidly lower the discharge pressure Pd, refrigerant is about to flow from the pressure-adjusting chamber 20 toward the high-pressure port 18 through the gap around the outer periphery of the pressure-sensing piston 19. In this regard, there is a difference in the flow rate of refrigerant flowing through the gap around the outer periphery of the pressure-sensing piston 19 between when the discharge pressure Pd has rapidly increased and when the same has rapidly decreased. When the discharge pressure Pd has rapidly increased, it takes a short time for the pressure in the pressure-adjusting chamber 20 to become equal to the discharge pressure Pd rapidly increased, whereas when the discharge pressure Pd has rapidly decreased, it takes a longer time for the pressure in the pressure-adjusting chamber 20 to become equal to the discharge pressure Pd rapidly decreased. A force which the pressure-sensing piston 19 exerts on the valve element 23 of the valve section 13 in the valve-closing direction when the discharge pressure Pd has rapidly increased is smaller than a force which the pressure-sensing piston 19 exerts on the valve element 23 in the valve-opening direction when the discharge pressure Pd has rapidly decreased, so that when the discharge pressure Pd has rapidly increased, the pressure-sensing section 12 becomes less sensitive, whereby the sensitivity of the valve section 13 is not much lowered. On the other hand, during a transition period over which the discharge pressure Pd rapidly decreases, the pressure-sensing piston 19 is easy to move in the valve-opening direction, and hence the pressure-sensing section 12 becomes more sensitive. Since the differential pressure between the discharge pressure Pd and the suction pressure Ps becomes smaller, a force that is about to cause the valve section 13 to operate in the valve-closing direction is instantaneously canceled by a force that is about to cause the pressure-sensing section 12 to operate in the valve-opening direction, the movement of the valve element 23 of the valve section 13 in the valve-closing direction is suppressed. As a result, the valve section 13 is inhibited from performing an excessive response in the direction in which the discharge pressure Pd is rapidly decreased. This prevents a high-sensitivity compressor from causing a hunting phenomenon due to a rapid change in the discharge pressure Pd.

FIG. 8 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a seventh embodiment of the present invention. In FIG. 8, component elements identical to those shown in FIG. 3 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 a according to the second embodiment in which the pressure-sensing section 12 senses rapid changes in the pressure Pc supplied to the crankcase in an increasing direction and a decreasing direction of the pressure Pc for control of the valve lift of the valve section 13, in the control valve 11 f according to the seventh embodiment, the pressure-sensing section 12 does not sense a rapid change in the pressure Pc supplied to the crankcase in the increasing direction but sensitively detects only a rapid change in the pressure Pc in the decreasing direction for control of the valve lift of the valve section 13.

More specifically, in the control valve 11 f, the pressure-sensing piston 19 as a component of the pressure-sensing section 12 is provided with a check valve mechanism for switching sensitivity between when a rapid change occurs in the pressure Pc supplied to the crankcase in the increasing direction and when a rapid change occurs in the same in the decreasing direction. The check valve mechanism is formed by forming a passage with a stepped portion in the pressure-sensing piston 19 for communication between the medium-pressure port 26 and the pressure-adjusting chamber 20, disposing the ball-shaped valve element 41 in a large-diameter passage toward the pressure-adjusting chamber 20, and fitting a stopper 44 in an open end of the passage toward the pressure-adjusting chamber 20 such that the valve element 41 is prevented from being removed into the pressure-adjusting chamber 20.

When the control valve 11 f constructed as above is controlling the compressor at a predetermined valve lift, if a rapid increase in the discharge pressure Pd causes the valve section 13 to operate in the valve-opening direction to thereby rapidly increase the pressure Pc supplied to the crankcase, the check valve mechanism provided in the pressure-sensing piston 19 is immediately opened by the differential pressure between the pressure Pc in the crankcase and the pressure in the pressure-adjusting chamber 20. Therefore, since the pressure-sensing section 12 does not adversely affect the operation of the valve section 13, the valve section 13 promptly operates in the valve-opening direction in response to the rapid increase in the pressure Pc to increase the pressure Pc in the crankcase more promptly, thereby promptly controlling the discharge capacity of the compressor in the decreasing direction.

Inversely, if the pressure Pc supplied to the crankcase has rapidly decreased, the pressure Pc in the medium-pressure port 26 becomes lower than pressure Pc(av) in the pressure-adjusting chamber 20, which is average pressure of the pressure Pc before it has rapidly decreased, whereby the check valve mechanism provided in the pressure-sensing piston 19 is closed. As a result, the pressure-sensing piston 19 having a larger pressure-receiving area than that of the valve element 23 sensitively detects the rapid decrease in the pressure Pc, and the differential pressure between the discharge pressure Pd and the suction pressure Ps becomes smaller, so that the operation of the valve section 13 in the valve-closing direction is instantaneously suppressed by the pressure-sensing section 12 sensitively acting in the valve-opening direction.

With this arrangement, the control valve 11 f is provided with asymmetric valve-opening characteristics that it has a high sensitivity to a rapid change in the pressure Pc supplied to the crankcase in the increasing direction, whereas it has a low sensitivity to a rapid change in the pressure Pc in the decreasing direction. This prevents occurrence of the hunting of the control even if the pressure Pc is rapidly changed due to the rapid change in the discharge pressure Pd.

FIG. 9 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to an eighth embodiment of the present invention. In FIG. 9, component elements identical to those shown in FIG. 4 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 b according to the third embodiment in which the pressure-sensing section 12 senses rapid changes in the suction pressure Ps in an increasing direction and a decreasing direction for control of the valve lift of the valve section 13, in the control valve 11 g according to the eighth embodiment, the pressure-sensing section 12 does not sense a rapid change in the suction pressure Ps in the decreasing direction but sensitively detects only a rapid change in the suction pressure Ps in the increasing direction for control of the valve lift of the valve section 13.

More specifically, in the control valve 11 g, the pressure-sensing piston 19 as a component of the pressure-sensing section 12 is provided with a check valve mechanism for switching sensitivity between when a rapid change occurs in the suction pressure Ps in the increasing direction and when a rapid change occurs in the same in the decreasing direction. The check valve mechanism is formed by forming a passage with a stepped portion in the pressure-sensing piston 19 for communication between the low-pressure port 27 and the pressure-adjusting chamber 20, disposing the ball-shaped valve element 41 in a large-diameter passage toward the low-pressure port 27, and fitting the stopper 44 in an open end of the passage toward the low-pressure port 27 such that the valve element 41 is prevented from being removed into the space communicating with the low-pressure port 27.

When the control valve 11 g constructed as above is controlling the compressor at a predetermined valve lift, if a rapid increase in the discharge pressure Pd causes a rapid decrease in the suction pressure Ps, the check valve mechanism provided in the pressure-sensing piston 19 is immediately opened by the differential pressure between the suction pressure Ps and the pressure in the pressure-adjusting chamber 20. Therefore, the pressure-sensing section 12 does not adversely affect the operation of the valve section 13, so that the valve section 13 operates promptly in the valve-opening direction in response to the rapid increase in the discharge pressure Pd to increase the pressure Pc in the crankcase more promptly, and promptly controls the compressor in a direction in which the discharge capacity thereof decreases.

Inversely, if a rapid decrease in the discharge pressure Pd causes a rapid increase in the suction pressure Ps, the suction pressure Ps in the low-pressure port 27 becomes higher than pressure Ps(av) in the pressure-adjusting chamber 20, which is average pressure of the suction pressure Ps before it has rapidly increased, so that the check valve mechanism provided in the pressure-sensing piston 19 is closed. As a result, the pressure-sensing piston 19 sensitively detects the rapid increase in the suction pressure Ps, and the operation of the valve section 13 in the valve-closing direction is instantaneously suppressed by the pressure-sensing section 12 which sensitively acts in the valve-opening direction.

With this arrangement, the control valve 11 g is provided with asymmetric valve-opening characteristics that it has a high sensitivity to a rapid change in the suction pressure Ps in the decreasing direction, and it has a low sensitivity to a rapid change in the pressure Pc in the increasing direction. This prevents occurrence of hunting.

The control valve for a variable displacement compressor, according to the present invention, is configured such that when the compressor undergoes a rapid change in the rotational speed thereof, the pressure-sensing section senses a change in pressure caused by the rapid change in the rotational speed of the compressor and makes the motion of the valve section in a valve-opening/closing direction slower by a value proportional to the degree of the change in pressure. This enables the control valve to perform stable displacement control without any hunting even when the high-sensitivity compressor experiences a rapid change in the rotational speed thereof.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents. 

1. A control valve for a variable displacement compressor, which is configured to sense differential pressure between discharge pressure in a discharge chamber of the compressor and suction pressure in a suction chamber of the compressor, and control a flow rate of refrigerant allowed to flow from the discharge chamber into a crankcase to thereby change a discharge capacity of the refrigerant, comprising: a pressure-sensing section that senses a change in pressure caused by a rapid change in a rotational speed of the compressor and makes a motion of a valve section in a valve-opening/closing direction slower by a value proportional to a degree of the change in pressure.
 2. The control valve according to claim 1, wherein the pressure-sensing section comprises a pressure-sensing piston that is disposed in a high-pressure port through which the discharge pressure is introduced, for receiving the discharge pressure at a pressure-receiving area larger than that of a valve element, and a shaft that transmits an axial motion generated by differential pressure between the discharge pressure and pressure in a pressure-adjusting chamber closed by the pressure-sensing piston which are received by the pressure-sensing piston, through a valve hole to the valve element.
 3. The control valve according to claim 2, wherein the shaft is formed integrally with the valve element that receives the discharge pressure at one end face thereof, and a piston rod that receives the suction pressure at an end face thereof opposite to the one end face.
 4. The control valve according to claim 2, wherein the pressure-sensing section further comprises sensitivity-switching means for making a force which the pressure-sensing piston causes to act on the valve element via the shaft smaller when the discharge pressure is rapidly increased than when the discharge pressure is rapidly decreased.
 5. The control valve according to claim 4, wherein the sensitivity-switching means is a check valve disposed in a passage formed through the pressure-sensing piston for communication between a side toward the high-pressure port and the pressure-adjusting chamber, for allowing flow of refrigerant from the side toward the high-pressure port to the pressure-adjusting chamber, and blocking flow of the refrigerant from the pressure-adjusting chamber to the side toward the high-pressure port.
 6. The control valve according to claim 4, wherein the sensitivity-switching means is a check valve provided in a passage that is formed through a member defining the pressure-adjusting chamber together with the pressure-sensing piston such that the passage communicates between a side receiving the discharge pressure and the pressure-adjusting chamber, for blocking flow of refrigerant from the side receiving the discharge pressure to the pressure-adjusting chamber, and allowing the refrigerant to flow from the pressure-adjusting chamber to the side receiving the discharge pressure.
 7. The control valve according to claim 4, wherein the sensitivity-switching means is formed by forming an outer periphery of the pressure-sensing piston into a tapered shape such that a gap formed as a passage along the outer periphery of the pressure-sensing piston is progressively decreased in cross-sectional area from the side toward the high-pressure port to the pressure-adjusting chamber.
 8. The control valve according to claim 1, wherein the pressure-sensing section has a pressure-sensing -piston disposed in a medium-pressure port through which control pressure controlled by the valve section is delivered into the crankcase, for receiving the control pressure at a pressure-receiving area larger than that of a valve element, and wherein the pressure-sensing piston is configured to transmit an axial motion caused by differential pressure between the control pressure and pressure in a pressure-adjusting chamber closed by the pressure-sensing piston which are received by the pressure-sensing piston, to the valve element.
 9. The control valve according to claim 8, wherein the pressure-sensing section further comprises sensitivity-switching means for making a force which the pressure-sensing piston causes to act on the valve element smaller when the control pressure is rapidly increased than when the control pressure is rapidly decreased.
 10. The control valve according to claim 9, wherein the sensitivity-switching means is a check valve provided in a passage that is formed through the pressure-sensing piston such that the passage communicates between a side toward the medium-pressure port and the pressure-adjusting chamber, for allowing refrigerant to flow from the side toward the medium-pressure port to the pressure-adjusting chamber, and blocking flow of the refrigerant from the pressure-adjusting chamber to the side toward the medium-pressure port.
 11. The control valve according to claim 1, wherein the pressure-sensing section has a pressure-sensing piston disposed in a low-pressure port through which the suction pressure is introduced, for receiving the suction pressure at a pressure-receiving area larger than that of a valve element, and wherein the pressure-sensing piston is configured to transmit an axial motion caused by differential pressure between the suction pressure and pressure in a pressure-adjusting chamber closed by the pressure-sensing piston which are received by the pressure-sensing piston, to the valve element.
 12. The control valve according to claim 11, wherein the pressure-sensing section further comprises sensitivity-switching means for making a force which the pressure-sensing piston causes to act on the valve element larger when the suction pressure is rapidly increased than when the suction pressure is rapidly decreased.
 13. The control valve according to claim 12, wherein the sensitivity-switching means is a check valve disposed in a passage that is formed through the pressure-sensing piston such that the passage communicates between a side toward the low-pressure port and the pressure-adjusting chamber, for allowing refrigerant to flow from the side toward the low-pressure port to the pressure-adjusting chamber, and blocking flow of the refrigerant from the pressure-adjusting chamber to the side toward the low-pressure port. 